Fine line geometries, common in semiconductor integrated circuits, are defined by radiation responsive resists which coat the surface of a semiconductor chip and, for example, polymerize in accordance with an exposure pattern projected at the surface of the chip. The nonpolymerized portion of the resist is removed leaving a pattern which acts as a mask to a subsequent diffusion step or as a mask to an etchant or to a metal deposition step. In these cases, a pattern of diffused, etched, or coated regions results respectively.
It is important that a semiconductor chip be used efficiently because more efficient utilization of the chip leads to a lower cost per bit or function performed. Naturally, an urgency exists to define functions in increasingly smaller areas of the chip.
Increasingly smaller feature size for devices in a chip is achieved by sophisticated processing including a faithful reproduction of a pattern in the resist. But a faithful reproduction requires an accurate master or mask. The problem to which the present invention is directed is to obtain a radiation-transparent film or window which is structurally stable and free of distortion over the ranges of common processing conditions so that radiation-opaque features, defined on such a film, can serve as a distortion-free radiation mask. Inasmuch as the mask is employed to pattern a beam of uniform radiation (i.e., optical or x-ray) it is also required that the mask allow that radiation to pass selectively to the surface of the resist where no opaque features exist to obstruct that passage.
Distortion free masks have been difficult to make hitherto because the windows have been made of thin films which respond differently to different processing conditions. An attempt to avoid distortion under such different conditions has led to lamellate, stress-compensated windows as disclosed in G. A. Coquin et al, U.S. Pat. No. 4,037,111.